weird wall question

[Valerie in NS]

Well, I started out replacing two living room windows... and while the trim was off, I decided to replace the wall panels... and finding out that there was only an inch or so of sprayed-in foam insulation, I decided to upgrade the insulation while I had the panels off... and in tearing out the old foam insulation, I discovered an oddity in my walls:

The exterior wall has a gap of about a foot between upper and lower sheets of plywood, where I can now see the aluminum siding from inside the room.

Is there a reason for this, or was it just a cost-saving measure?

Even though over the aluminum siding there is now a layer of foamboard insulation and then vinyl siding, when it's windy, I can feel the draft through this opening (I'm having trouble finding insulation, so the walls have been exposed for a week or so now).

I was going to use silicone and seal the gaps between the plywood and the aluminum to try to block some of this airflow, but thought I should ask just in case there is a reason I shouldn't - this is not only my first mobile home, but also the first home I've had to do any repair work on myself so I'm worried about screwing up!

I took pics to show what I was talking about, but I don't know how to get them to show up here, so I'll see if I can put them in my profile somewhere...

[shadow745]

Well part of home ownership is screwing up something because as you go along you learn from mistakes and learn how to do things better and more efficiently.

That does look kind of strange. I wouldn't say normal maybe there was a lack of material or effort. Kind of like I've seen in a site built home. If you have 8.5 ft. ceilings and 8 ft. sheetrock then those gaps will usually be covered by crown molding and baseboard. Not many people take the time to fill in all the spaces.

Those wall studs look a little flimsy from you pics? Not 2x4s are they? What is the standard in a mobile? Later!

[Greg]

A home that age most likely had the aluminum siding screwed directly to the studs. I would guess that over the years someone added a plywood underlay. I'm not sure why they left a gap, but just a guess would be to allow for some ventilation. If it is dry in there and you don't have major drafts I would be tempted to leave it. Greg

[Valerie in NS]

Those wall studs look a little flimsy from you pics? Not 2x4s are they? What is the standard in a mobile? Later!

Shocked me when I saw what they are: 2x3s! caused some cursing, given that I hadn't even imagined that when ordering my new windows. Fortunately it only took a little ingenuity to make them work.

I don't know what was standard when this thing was built. I'm just amazed that these things didn't fall apart on the highway!

[Valerie in NS]

If it is dry in there and you don't have major drafts I would be tempted to leave it. Greg

Well, we had a lovely little storm here, and with the walls open I can now definitively state that there ARE major drafts through that gap! LOL

Since there is some sort of half inch strapping on the inside of the plywood, I've decided to use 1/2 foam board as a layer of insulation, which will cover the gap and seal out the wind. (The main insulation will be 2" mineral wool - easier to put the 1/2 foamboard in than try to cut 1/2 out of the mineral wool to allow for the strapping - plus the fact that at the moment I can *get* 2" mineral wool but the 2.5" is on 14-16 week back order!)

[Greg]

2x3 was the standard back then, that's before HUD got involved with federal standards. Glad you had a chance to open up the walls and get a look at what is really going on in there. The foam should help.

If it is metal strapping inside the walls it could be either tie down straps or if it runs diagonal it could be to make the wall stiffer. Greg